A view of the U.S. Senate building and the Capitol dome in Washington, D.C. / Tim Sloan, AFP/Getty Images

by Alan Fram, Associated Press

by Alan Fram, Associated Press

WASHINGTON (AP) - The U.S. Congress returns Monday from a two-week recess with gun control legislation high on the Senate's agenda as President Obama looks for a breakthrough in his efforts to curb gun violence following the December massacre at a Connecticut school.

The administration moved quickly after the shooting amid concerns that the high emotions would settle and politics would go back to normal on one of the country's most sensitive issues. The country's top gun lobby has opposed the gun control drive, and the president's proposals have weakened in the months since the shooting amid fears that the more controversial ones, such as an assault weapons ban, will harm an overall gun control package.

On Monday, Obama travels to Connecticut to again make the case for gun legislation.

Senators could start debating gun legislation before week's end, but leaders might take more time to seek a breakthrough deal on expanding background checks for gun buyers - the proposal seen as having the best chance of passage.

Two influential senators, one from the Democrats and one from opposition Republicans, are working on an agreement that could expand background checks on firearms sales to include gun shows and online transactions, Senate aides said Sunday.

Federal background checks are currently required only for transactions handled by the roughly 55,000 federally licensed firearms dealers. Private sales such as gun show or online purchases are exempt. The system is designed to keep guns from criminals, people with serious mental problems, some drug abusers and others.

After the Connecticut massacre, Obama proposed applying the requirement to virtually all firearms sales. Gun control advocates consider expanded background checks to be the most effective step lawmakers could take to curb gun violence.

The NRA and other critics say the checks are ignored by criminals, and they fear that expanding the system could be a step to the government maintaining files on gun owners.

Democratic Sen. Joe Manchin and Republican Sen. Pat Toomey could reach an accord early this week, said the aides, who spoke on condition of anonymity to describe the private talks.

Manchin is a moderate who touts a top "A'' rating from the National Rifle Association, the influential gun rights lobbying group which has led the opposition to Obama's gun control drive. Toomey has solid conservative credentials.

Their united front would make it easier for gun control advocates to attract support from moderate Democrats who have been wary of supporting the effort and from Republicans who have largely opposed it so far.

With conservative Republicans threatening to use legislative maneuvers to prevent a final vote on gun control legislation, Democrats will need 60 of the chamber's 100 votes to prevail. There are 53 Democrats and two Democratic-leaning independents in the Senate.

Sen. John McCain urged his fellow Republicans to allow debate on gun legislation to go forward without the maneuver. However, he declined to express support for an expanded background check bill.

Other Obama gun control priorities include banning assault weapons and ammunition magazines with more than 10 rounds. Both bans are expected to be offered as amendments, but the assault weapons ban seems sure to be defeated, and the high-capacity magazine prohibition also faces difficult odds.

Gun control advocates are worried their allies might cut a deal that goes too far.

"We want a vote on the issues. We don't want them watered down so they're unrecognizable," said Josh Horwitz, executive director of the Coalition to Stop Gun Violence. "If they can't vote for it, let the American people judge them on that. Don't let a dumbed-down bill be the outcome of this."

Justice Department figures show that from 1994, when the current background check system began, through 2010, 118 million potential gun buyers were checked and 2.1 million were denied firearms. Defenders say the data proves the checks prevent many dangerous people from getting weapons.

With or without an agreement, the Senate gun legislation would toughen federal laws against illegal firearms sales, including against people who buy firearms for criminals or others barred from owning them. The legislation also would provide $40 million a year, a modest increase from current levels of $30 million, for a federal program that helps schools take safety measures such as reinforcing classroom doors

Also high on Congress' agenda as it returns is immigration, where a decisive moment is approaching.

Bipartisan groups in the House and Senate are expected to present legislation as early as this week aimed at securing the U.S. border, fixing legal immigration and granting legal status to the estimated 11 million who are in the United States without authorization. That will open months of debate on the issue.

Lawmakers will also devote time to the 2014 budget that Obama plans to release Wednesday. It calls for new tax increases, which Republicans oppose, and smaller annual cost-of-living increases in Social Security pension payments to retirees and other government benefit programs, over the objections of many of the president's fellow Democrats..

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